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Product Group

Ketones

General Information concerning the product group

Ketones

During water determination after Karl Fischer (KF) aldehydes and ketones cause side reactions with the normally utilised methanol. Both side reactions, i.e. the formation of acetals and ketals, as well as bisulphite addition, can often be recognised by dragging end points and lead to wrong results. During acetal or ketal formation water is released which simulates water contents that are too high. Bisulphite addition, however, consumes water, leading to results that are too low. The extent of the interferences depends on the reactivity of the substances as well as the reactivity of the utilised KF solutions. Through utilisation of specific KF reagents for aldehydes and ketones it is possible to largely suppress the side reactions. The coulometric method is not recommended.

Special Information concerning the sample and the methods

Aromatic groups reduce the reactivity of ketones in KF solutions. The influence of disturbing side reactions for this substance is therefore less characteristic than for acetone. KF titration is carried out with methanol-free reagents, whereby two alternatives are at hand: CombiTitrant 5 Keto + CombiSolvent Keto, or CombiTitrant 2 + CombiSolvent.

Procedure: The titration medium is first placed into the cell and titrated dry by means of the titrant. Then the sample is added with a syringe (exact sample weight determination by weighing of syringe before and after injection) or volumetric pipette and the titration is started.